"We found that after rain-forest conversion to agricultural pastures, bacterial communities were significantly different from those of forest soils," microbiologist Klaus Nusslein from the University of Massachusetts Amherst, said.
"Not only did the pasture soils show increased species numbers, these species were also less related to one another than in rain-forest soil.
"This is important because the combination of lost forest species and the homogenisation of pasture communities together signal that this ecosystem is now a lot less capable of dealing with additional outside stress," said Nusslein, an expert in tropical rain forest microbial soil communities.
Researchers studied a large farm site over the past four years at the frontier where farmers drive agriculture into pristine rain-forest in Rondonia, Brazil, to convert rain-forest to agricultural use.
Findings in part validated previous research showing that bacteria in the soil became more diverse after conversion to pasture.
The study shows that the loss of restricted ranges for different bacteria communities results in a biotic homogenisation and net loss of diversity overall.
Scientists have warned that the loss of genetic variation in bacteria across a converted forest could reduce ecosystem resilience.
"We have known for a long time that conversion of rain-forest land in the Amazon for agriculture results in a loss of biodiversity in plants and animals. Now we know that microbial communities which are so important to the ecosystem also suffer significant losses," said biologist Jorge Rodrigues from the University of Texas, in a statement.
Amazon represents half of the world's rain-forest and is home to one-third of Earth's species, yet the Amazon has one of the highest rates of deforestation, researchers point.
